This invention relates to a flow control valve and more particularly to a flow rate control valve suitable for use with a throttle valve of an internal combustion engine.
FIG. 1 illustrates a conventional flow rate control valve used as a bypass flow path of an engine. In FIG. 1, reference numeral 1 designates a throttle body defining a horizontally extending air suction passage, 2 is a throttle valve for opening or closing the passage within the throttle body 1, 3 is a valve shaft movably supporting the valve 2 and extending perpendicularly to the suction passage, 4 is a barrier wall formed in the inner lower portion of the throttle body 1, 5a and 5b are bypass passages formed in the bottom of the throttle body 1, and 5c is a bypass opening in communication with the bypass passage 5b and located at a level higher than the central axis of the throttle body 1 in an inner circumference of the cylindrical wall of the throttle body 1.
The flow rate of the air flowing into an engine (not shown) from the air suction passage of the throttle body 1 in the direction of an arrow A is controlled at will in accordance with the opening of the throttle valve 2. The fuel is injected from the fuel injection valve in accordance with the above air flow rate to be supplied to the engine as a mixture. In order to ensure that the engine rotational speed is maintained at a target speed, a proportional solenoid valve 9 which is a flow rate control valve controls an auxiliary air flow through the bypass passages 5a and 5b including the bypass opening 5c.
A valve housing 15 of the proportional solenoid valve 9 is hermetically mounted to the lower portion of the throttle body 1 and comprises an air inlet 28a and an outlet 28b. The auxiliary air flows from the bypass passage 5a through the air inlet 28a, fluid flow ports 31 formed in a cylindrical wall of a hollow cylinder 32 disposed within the valve housing 15, the space within the cylinder 32, the air outlet 28b and through the bypass passages 5b and 5c. In order to adjust the open area of the opening of the fluid flow ports 31, a valve body 41 is slidably inserted as a movable iron core within the hollow cylinder 32. A compression spring 43 is disposed between the front end of the valve body 41 and the spring holder 6, and a compression spring 42 is mounted between the rear end of the valve body 41 and the stationary iron core 7. Around the cylinder 32, a solenoid coil 40 wound around a bobbin 8 is mounted. Reference numeral 44 designates a recess formed in the bottom of the inner circumferential surface of the throttle body 1.
In the conventional arrangement as above described, the solenoid coil 40 is energized by an electric current in accordance with a deviation of the measured rotational speed with respect to the target rotational speed by an unillustrated electronic control circuit, so that the valve body 41 advances or retracts proportionally to the applied current value to adjust the open area of the fluid flow ports 31. Therefore, the amount of the air flow through the bypass passages 5a and 5b is controlled so that the engine rotational speed equals to the target speed, and the amount of the fuel to be injected is also controlled accordingly.
However, when the conventional flow control valve of the above construction is used for controlling air flow in the throttle valve of an internal combustion engine, foreign matters such as carbon particles or the like entrained in the fluid flowing through the throttle accumulate on the inner surface of the cylinder 32 and the outer surface of the valve body 41 and are caught therebetween, preventing the movement of the valve body 41.
Also, since the fluid flow ports 31 are formed by punching the metallic wall of the cylinder 32, the cylinder 32 can be easily deformed when the fluid flow ports 31 are being punched, impeding a smooth movement of the valve body 41 in the cylinder 32.